Continuous enamelware manufacture



H. T. BEBE CONTINUOUS ENAMELWARE MANUFACTURE Flled OCl 12, 1932 Patented Mar. 24, 1936 y STATES PATENT GFFICE CONTINUOUS ENAMELWARE MANUFACTURE Application October 12, 1932, Serial No. 637,440

17 Claims.

My invention relates to the continuous manufacture of vitreous enamel ware, and more particularly to an improved method of making mottled gray ware with a single coat of vitreous enamel; as, for instance, cooking or kitchen utensils made of sheet steel coated with a vitreous enamel to protect the metal from rusting and from the action of acids in use.

In the manufacture of such enamel ware, a liquid enamel coating is first applied to the Ware, usually by dipping, and the dipped ware is then dried; and to obtain a uniform mottled effect, it has been discovered that the drying must be done by exposing the free surface of individual pieces to the atmosphere, under controlled conditions of different relative movements, temperatures and humidities in substantially immediate successive periods of time during which the drying is being effected, to form and merge together the comparatively small rust spots or blotches of different colors or shades, which are required for producing the desired appearance.,

in the usual method of making such Ware, the dipped pieces have been placed on stationary racks located in a. drying room, through which heated air has been moved; and after the ware was suiciently dried, it was then burned in a furnace, which requires a manual transfer from drying rack frames to burning rack frames, for which as many as seven men were sometimes employed in actual practice.

The problem of making uniformly mottled enamel Ware products has been diicult to solve, no doubt, because even though sheet metal of the proper grain structure, analysis and cleanliness is coated with a liquid vitreous enamel of the proper composition and consistency, the mottled effect is obtained by a rusting or oxidation in spots or portions of the surface of the metal by certain ingredients or moisture of the enamel coating; and a control of the size and a merging of the spots can only be obtained by'peculiar and exact drying operations under certain conditions of time, and of the movement, the temperature, and the humidity of the atmosphere to which the ware, with the enamel coating thereon, is exposed during successive drying periods.

For the purpose of obtaining the best results in making enamel ware, it is preferred to select' pickled and annealed rollediron or st'eel sheets, which may be of from 24 to 30 gauge, known to the trade as P & A Enamel Stock, having a uniform average size of grain structure, and having a composition or analysis and ductility which permits a deep drawing of the sheet metal,

(Cl. S11-73) The enamel stock is first stamped or drawn into the desired shape for a cooking utensil or other article, from which all grease and surface dirt is removed by an alkali solution at a boilingr temperature, and all oxidation is then removed by a sulphuric acid pickling solution at a temperature of from 140 to 180 F.; after which all trace of acid is removed by Washing in clear run-- ning water, and the surface is neutralized and further oxidation avoided until the shapes are coated, by another alkali bath at a temperature or from 140 to 150 F.; which is followed by a quick drying in an ovenv hot enough to completely remove all moisture from the surface of the shapes, within four or iive minutes; after which the same are ready for theapplication of a liquid vitreous enamel.

There are many liquidvitreous enamels in common use, and a Well known formula may be followed, which includes a mixture of borax, 60 pounds; feldspar, 56 pounds; silica., 40 pounds; saltpeter, 3 pounds; soda ash, 20 pounds; fluor spar, 12 pounds; antimony, 3 pounds; cryolite, 10 pounds; bone ash, 6 pounds; and manganese oxide, 12 pounds; the same being smelted at about. 2200 F. into molten glass, Which is shattered into small fragments by being run out of the smelter into cold Water, and then ground in a ball mill for some twelve hours, wherein ballclay and water are added, to form a liquid enamel coating of about the consistency of thick cream.

The cleaned, pickled, and neutralized sheet steel shapes or pieces of ware are taken from the quick drying oven by the dipping operator and individually immersed in the liquid enamel solution, wherein it is given a single coating; the piece being suitably rotated and manipulated by the operator to give it a uniform single coating or covering of a singlethickness of the liquid enamel which adheres to the surface of the shape.

The liquid coating on the metal Ware is then ready for drying and burning, and according to the improved method, the drying operationsl include a continuous series in substantially immediate succession of several more or less distinct time periods, during which the drying is effected under different conditions of movement, temperature, and humidity of the atmosphere, in and by which the drying is effected. r

During the first drying period, the liquid coating on the Ware may be exposed for from twenty to twenty-rive minutes to the atmosphere, by slowly moving the ware in the ordinary atmosphere and air currents normally present in the drying room of an enamel ware manufacturing plant, which may have a temperature of from 70 to 90 F., with a normal degree of humidity, depending upon the season of the year; the period of the exposure being such as to gradually dry the wet enamel coating until it is fixed or set on the surface of the sheet metal, and until an oxidation resulting from the rusting of the metal by the wet coating, becomes visible in the form of small spots, more or less scattered, in some portions of the pieces of Work.

During the second drying period, the enamel coating on the work may be exposed for some thirty-five to forty minutes in a constantly movlng and actively agitated atmosphere, heated to a temperature according to a dry bulb reading of from to 115 F. and according to a wet bulb reading of from 65 to 85 F., at a humidity of approximately 25% to 35% of saturation, until most of the moisture is removed from the enamel coating which has been set during the first period; the exposure being extended during such a period as will initiate the oxidation or rusting of small adjacent spots to form and merge together in a uniform manner throughout the entire surface of each one of the coated shapes.

During the third drying period, the enamel coating on the ware may be exposed for from ve to ten minutes in a moderately moving atmosphere, heated to a temperature from to F., with a normal degree of humidity; and this period may be extended until the formation and merging of comparatively small adjacent oxide or rust spots has been completed throughout the entire surface of each enamel coated shape, but before the moisture has been entirely eliminated to produce a bone dry enamel coating.

And during the fourth drying period the enamel coating on the ware may be exposed for from five to ten minutes in a moderately moving atmosphere, heated to a temperature of from 160 to 200 F., with a normal degree of humidity; and this period is extended until the moisture in the enamel coating has been so completely eliminated as to produce a bone dry condition of the same; in which condition the enamel coated ware is ready for the final step of burning.

It will be understood, however, that the third and fourth drying periods are so nearly alike, that they may be considered together as a single period, during which the enamel coating may be exposed for from ten to twenty minutes in a moderately moving atmosphere, heated to a ternperature of from 140 to 200 F., with a normal degree of humidity; and such period is extended until the formation and merging of comparatively small adjacent rust spots has been completed throughout each enamel coated shape, and the moisture in the enamel coating has been so completely eliminated as to produce a bone dry condition of the same.

And it will be understood that the several conditions and degrees described for the substantially immediate successive periods of drying may be modified from the ranges which have been enumerated, depending upon different atmospheric conditions during the various seasons, and upon variations in the details of the composition of the liquid enamel coating, and more particularly, upon variations in the degree of one feature with respect to another, during the several drying periods; the described conditions being illustrative of those conditions which an extended experience in the actual use of the improved method, has resulted in the very successful production of single coated uniformly mottled enamel ware, as described.

In the final step of burning, the enamel coated ware may be exposed during a period of from ten to twelve minutes, beginning and ending with an initial and final temperature of some 700 F., for about four minutes each, and including an intervening maximum temperature of from 1200 to 1640 F. for about four minutes; the period of the burning exposure being extended until the enamel coating which has been completely dried, is completely vitrified on the metal base or body of the ware; and because of the described manner in which the enamel coating has been dried, the vitried coating presents a substantially uniform mottled appearance of closely adjacent small spots merged together.

During the drying and burning periods thus described, the enamel coated shapes may be continuously carried from the drying room through a series of successive drying zones or chambers and a burning furnace, and back into the drying room for cooling, by being individually mounted by the dipping operator upon racks depending from a continuously operating endless chain conveyer.

The continuous method thus described may be carried out by the apparatus which is disclosed in my copending application filed January 22, 1931, Serial No. 510,447, matured in Letters Patent No. 1,890,897, for Continuous enamel ware apparatus; the present application being a continuation in part of the common subject matter disclosed in that application, which is a copending continuation in part of the common subject matter disclosed in my earlier application filed May 13, 1929, Serial No. 362,834, for Continuous enamel ware manufacture; and such apparatus is illustrated in the accompanying drawings rforming part hereof, in which- Figure 1 is a diagrammatic plan View of the apparatus;

Fig. 2, an enlarged fragmentary diagrammatic transverse sectional View thereof, as on line 2--2, Figs. 1 and 3;

Fig- 3, an enlarged fragmentary longitudinal sectional View thereof, as on line 3 3, Figs. 1 and 2; and

Fig. 4, a diagrammatic outline plan of the apparatus.

Similar numerals refer to similar parts throughout the drawings.

The apparatus may include a dryer I0 and a furnace I I which are preferably located in a zone I2, which may be located in an enclosed room, such as the ordinary drying room of an enamel ware manufacturing plant.

A dryer I0 is preferably built of refractory walls I3 which may form a plurality of successive communicating zones or chambers I4, I5 and I6; and the first zone or chamber I 4 of the dryer, communicates with the zone I2 in which the dryer as a whole is located, as by means of an inlet passageway I 'I formed in the dryer walls.

For conserving space, the drying chambers I4, I5 and I6 are preferably located side by side, the chambers I4 and I5 having a common parti tion wall I8, and the chambers I5 and I6 having a common partition wall I9; with communicating openings 20 and 2I in the respective walls at opposite ends of the dryer, between the adjacent chambers.

The inlet passageway I'I, as illustrated, is preferably provided at one end corner of the dryer I0; and at the delivery end of chamber I6 may be provided an end closure wall 22 having formed therein an outlet opening 23 for the dryer.

This outlet opening 23 may communicate with the zone I2, as.illustrated, and one end wall of the burning furnace II may be located directly opposite the end wall 23 of the chamber I6; and the furnace wall 24 has formed therein an inlet opening 25 opposite the outlet opening 23 of the dryer, and the furnace wall 24 has also formed therein an outlet opening 26 laterally spaced from the opening 25; or, if desired, the dryer may communicate directly with the furnace.

A continuous endless chain conveyer 21, or the like, passes through the inlet passageway I1 into the dryer and through the successive chambers thereof, thence through the dryer outlet opening 23, and through the furnace inlet opening 25 into the interior 28 of the furnace and thence out of the furnace outlet opening 26 into the zone I2, and thence back to the dryer.

As illustrated, the rst drying chamber I4 has a greater volume than the successive drying chambers, for accommodating therein substantially 4 times the length of chain conveyer as is accommodated in the chamber I5, and the chamber I6 has a volume less than the volume of the chamber I5 for accommodating less length of the chain conveyer; and the entire length of the dryer may be approximately one hundred and fifty feet, for the purposes of the present invention.

Accordingly, with a constant speed of travel of the chain conveyer 21, which speed may be from 14 ft. to 20 ft. per minute, the enamel coated shapes indicated generally by 29 and carried. by the conveyer, as by means of racks 30 depending from the conveyer 21, are subject for different periods of time to the successive atmospheres of the successive zones or chambers.

Means are provided for maintaining the substantially immediate successive zones or chambers of the apparatus yat different temperatures, for maintaining differently directed blasts of air in each drying chamber and for maintaining different humidities in each drying chamber.

The temperature of the zone I2 as aforesaid may be the temperature of the ordinary drying room of an enamel ware manufacturing plant, and may be from '10 to 90 F. The temperature of the drying chamber or zone I4 is preferably maintained for the purposes of the present invention, at 65 to 85 F. wet bulb reading, and at 90 to 115 F. dry bulb reading, with a humidity of from 25% to 35% of saturation. 'Ihe temperature of the drying chamber or zone 15 is maintained at from 140 to 160 F., and the temperature of the drying chamber or zone I 6 is maintained at from 160 to 200 F.

'Ihe interior of the furnace 28 may be maintained at its end adjacent the inlet opening 25 and the outlet opening 26, at substantially '100 F., and at the other burner end of the furnace, the temperature is preferably from 1200 to 1640 F.

While the heating means and the air moving means for the drying chambers may be separate, in the embodiment illustrated in the drawings, common heating and air blasting means are provided by blowing or blasting hot air through the several chambers.

All the chambers of the dryer I0 may have a common bo-ttom wall 3| which is likewise the top wall of an exhaust chamber 32. The wall 3| has a plurality of openings 33 formed therein for each of the chambers I4, I5 and I6 for providing a communication between each drying chamber and the exhaust chamber 32.

Vertically directed blasts of hot lair are supplied to the drying chamber I4 as by means of a blower 34 whose inlet duct 35 is connected with a source of hot air, and whose outlet duct 36 communicates with the top of the chamber I4 through a plurality of branch outlet ducts 31.

'Ihe chambers or zones I5 and I6 are maintained at their differential temperatures and provided with vertical blasts of air as by means of a blower 34 whose inlet duct 35 is connected with Va source of air hotter than the source for the blower 34, and whose outlet duct 36 communicates with the upper portions of the chambers I5 and I6 through branch ducts 31'a and 31b, respectively, the ducts 31'by having th'e greater capacity.

One or more booster'or exhaust fans 38 may be located in the exhaust chamber 32 for facilitating drawing the differentially heated air vertically through the several drying chambers I4, I5 and I5; and a plurality of horizontally directed fans 4f! may be located in the several drying chambers near the bottom thereof for moving differently directed blasts of air therein; and/or a plurality of downwardly inclined directed fans 49' may be located near the top of the several drying chambers, at one end thereof, for blowing air currents downward toward the other end thereof, and into the open upper side of the several pieces of ware.

The humidity of the several drying chambers is separately controlled both by the relative volumes of the chambers, and by the use of a supply of water, which may be contained in pans 4I located in the chamber I4; or the humidity of the atmosphere may be increased or decreased by the use, or non-use, of steam sprays 42 fro-m an apertured steam pipe 42', as shown in the upper middle portion of the more humid chamber I4.

It will be understood that some of the Walls of the several drying chambers may have doors or shutters therein or may be entirely open at one end, as indicated at 43 and 44 in Fig. 4, for the more humid chamber I4; because such openings may be desirable for supplying a greater volume of the moving atmosphere which is highly heated and humidied for the purpose of the second period of drying carried on in the particular chamber.

The different periods of drying are provided, because of the precise conditions of time, temperature and humidity, which are required for initiating a uniformly mottled rusting of the metal by the wet coating; and although the rst period of drying may proceed in ordinary atmospheric conditions until scattering rust spots are visible, a further drying under the same conditions results in the formation of relatively large rust spots, blotches or streaks, which are not only unsightly, but the rust penetrates so deeply into the metal as to form depressed spots or streaks when the ware is burned.

For that reason, the drying during the second period is retarded, by increasing the humidity of. the atmosphere, and at the same time a uniformly mottled rust is facilitated, by increasing the temperature of the atmo-sphere; so that the mottled rusting is initiated throughout the entire surface of each shape, as well as throughout the entire surface of the many different sizes of shapes which may be continuously and contemporaneously dried and burned by the present method.

In other words, there must be a changein and a coordination between the time, the temperature and the humidity, after small scattering rust spots begin to form, until adjacent small rust spots are formed and merge throughout the entire surface of each shape, as well as of many diierent sizes and kinds of shapes, which may include various kitchen utensils, from small cups, stew pans and coffee pots, to very large dish pans and the like.

There must also be a substantially continuous and substantially immediate succession of the several drying periods, and preferably of the burning period; because an exposure to the ordinary atmosphere for any considerable length of time between the first and second drying periods, will result in an excessive and a non-uniform oxidation or rusting; and an exposure to the ordinary atmosphere between the second and third, and the third and fourth drying periods, for any considerable length of time, will also result in an excessive oxidation and a non-uniform completion of the mottled rusting which has been initiated during the second period.

And likewise, if the bone dry ena-mel coating at the completion of the drying operations is exposed to the ordinary'atmosphere for any considerable length of time, it will absorb moisture therefrom, which will cause a further and an excessive oxidation, and destroy the uniform mottled rusting which has been effected, as described, and which can only be preserved by promptly burning the ware, for accomplishing the purposes of the present invention.

And nally, the continuous movement of the ware, from the time it is dipped and placed upon the endless conveyer racks, until it has been dried and burned to produce the nished product as described, and until the same has been cooled and removed to ware trucks; avoids the loss of marred ware, which always results from a manual handling of the individual shapes to and from carrying boards, trays, trucks and the like, in common practice.

Such a marring causes a loss of defective ware, which may amount to from 10% to 15% of the entire production; and it is diicult, if not impossible, to avoid the same, because the smooth, wet enamel coating is so delicate that it is impaired and defaced by the slightest touch of the hand of an operator, or a contact with an adjacent piece of ware or other object; and the bcne dry coating is merely a thin film of the powdered enamel, which is likewise disgured and damaged, if not entirely removed, by the touch or contact of a hand or another object.

In addition to the saving of loss from damaged ware, the continuous movement of the enameled shapes upon an endless conveyer, in substantially immediate succession throughout the drying and burning periods, saves the time and expense of the labor which would otherwise be required for handling the Ware during these operations; and because the dipping, burning, drying, cooling and removing operations are all continuously coordinated and completed within an hour and a half, there is no loss of labor or delay in production, which frequently occurs when one or more of the several periods of manufacture are independently or separately carried on, as in common practice.

I claim:-

1. The method of making mottled enamel ware, which consists in drying a wet enamel coating upon a sheet steel shape by exposing the same in an ordinary atmosphere at a temperature of from 70 to 90 F., for from 20 to 25 minutes; then exposing the same in an actively moving atmosphere at from 65 to 85 F. wet bulb reading and from 90 to 115 F. dry bulb reading, that is with a humidity of from 25% to 35% of saturation, for from to 40 minutes; then exposing the same to a moderately moving atmosphere at from 140 to 160 F., for from 5 to 10 minutes; then exposing the same in an atmosphere at from 160 to 200 F., for from 5 to 10 minutes; and then burning the enamel coated shape.

2. The method of making mottled enamel ware, which includes drying single wet enamel coatings upon sheet steel shapes by exposing the same in an ordinary atmosphere until small scattered rust spots are visible, then promptly exposing the same in a heated humid moving atmosphere until the forming and merging of small adjacent rust spots is initiated throughout the surfaces of the shapes, then promptly exposing the same in a higher heated moving atmophere until the forming and merging of the rust spots is completed, then promptly exposing the same to a higher heated atmosphere until the enamel coating is bone dry, and then promptly exposing the ware to a burning atmosphere, all while moving the shapes continuously through each and all of the atmospheres.

3. The method of making mottled enamel ware, which includes drying a wet enamel coating upon a sheet steel shape by exposing the same in an ordinary atmosphere until small scattered rust spots are visible, then exposing the same in a heated humid moving atmosphere until the forming and merging of small adjacent rust spots is initiated throughout the surface of the shape, then exposing the same in a higher heated moving atmosphere until the forming and merging of the rust spots is completed, then exposing the same to a higher heated atmosphere until the enamel coating is bone dry, and then burning the enamel coated shape.

4. The method of making mottled enamel ware, which includes drying a wet enamel coating upon a sheet steel shape by exposing the same in an ordinary atmosphere until small scattered rust spots are visible, then exposing the same in a heated humid moving atmosphere until the forming and merging of small adjacent rust spots is initiated throughout the surface of the shape, then exposing the same in a higher heated moving atmosphere until the forming and merging of the rust spots is completed, and then exposing the same to a higher heated atmosphere until the enamel coating is bone dry.

5. The method of making mottled enamel ware, which includes drying a wet enamel coating upon a sheet steel shape, by exposing the same in an ordinary atmosphere until small scattered rust spots are visible, then exposing the same in a heated humid moving atmosphere until the forming and merging of small adjacent rust spots is initiated throughout the surface of the shape, and then exposing the same to a higher heated atmosphere until the forming and merging of the rust spots is completed and the enamel coating is bone d ry.

6. The method of making mottled enamel ware, which includes the steps of drying a wet enamel coating upon a sheet steel shape by exposing the same in a heated humid moving atmosphere until the forming and merging of small adjacent rust spots is initiated throughout the surface of the shape, and then exposing the same to a higher heated moving atmosphere until the forming and merging of the rust spots is completed and the enamel coating is bone dry.

7. The method of making mottled enamel ware, which includes the steps of drying a Wet enamel coating upon a sheet steel shape, by exposing the same in an ordinary atmosphere until small scattered rust spots are visible, and then exposing the same in a heated humid moving atmosphere until the forming and merging of small adjacent rust spots is initiated throughout the surface of the shape.

8. The method of making mottled enamel Ware which includes the step of drying a Wet enamel coating by exposing the same in an actively moving atmosphere at from 60 to 85 F. wet bulb reading, and from 90 to 115 F. dry bulb reading,

that is, with a humidity of from 25% to 35% of v saturation, for from 35 to 40 minutes.

9. The method of making enamel sheet steel Ware and the like, Which includes continuously moving and subjecting such ware having liquid enamel applied thereon to immediately successive drying atmospheres, beginning with the ordinary temperature of a drying room and each successive atmosphere being independently maintained at substantially higher drying temperature than the previous atmosphere toi uniformly form and then merge comparatively small adjacent rust spots throughout the surface of the ware, and then burning the ware.

l0. The method of making enamel sheet steel Ware and the like, Which includes continuously moving and subjecting such ware having liquid enamel applied thereon to ordinary atmospheric conditions for a substantial length or time and then to immediately successive drying atmospheres, each drying atmosphere acting on the Ware for a substantial length of time, and each atmosphere being independently maintained at a substantially higher drying temperature than the previous atmosphere to uniformly form and then merge comparatively small adjacent rust spots throughout the surface of the Ware.

11. The method of making enamel sheet steei Ware and the like, which includes continuously moving and drying such Ware having liquid enamel applied thereon, by subjecting the Ware in immediate succession to blasts of heated air, beginning with the ordinary temperature of a drying room and each successive blast being maintained at a substantially higher temperature than a previous blast.

12. The method of making enamel sheet steel Ware and the like, which includes continuously moving and subjecting such ware having liquid enamel applied thereon to immediately successive drying atmospheres, beginning with t-he ordinary temperature of a drying room and each successive atmosphere being independently maintained at a higher drying temperature With a different degree of humidity, than the previous atmosphere.

i3. The method of making enamel sheet steel ware and the like, which includes continuously moving and subjecting such Ware having liquid enamel applied thereon to ordinary atmospheric conditions for a substantial length of time, and then to immediately successive drying atmospheres, each atmosphere acting on the Ware for a substantial length of time and each atmosphere being independently maintained at a higher temperature with a dif-ferent degree of humidity than the previous atmosphere.

14. The method of making enamel sheet Steel Ware and the like, which includes continuously moving and drying such ware having liquid enamel applied thereto, and subjecting the ware in immediate succession to differently directed blasts of heated air, beginning with the ordinary temperature of a drying room andA each successive blast being maintained at substantialiy higher drying temperatures than a previous blast.

l5. The method ci making enamel sheet steel Ware and the like, which includes continuously moving and drying liquid enamel on such Ware by subjecting the Ware in immediate succession to lasts off air, beginning with the ordinary temperature of a drying room and each successive blast being maintained at a substantially higher drying temperature with a different degree of humidity than a previous blast.

16. The method of making enamel sheet steel Ware and the like, which includes continuously moving and drying a Wet enamel coating on such Ware in a normal atmosphere until scattered rust spots appear, then facilitatingthe forming and merging of rust spots While retarding the drying in a higher than normal drying heat and degree orf humidity, and then completely drying the coating in a still higher atmospheric heat.

i7. The method of making enamel sheet steel Ware and the like, which includes continuously moving and drying a Wet enamel coating thereon in normal atmosphere until scattered rust spots appear therein, then facilitating the forming and merging of rust spots While retarding the drying in a higher than normal drying heat and degree of humidity, and then completely drying the coating in a still higher atmospheric heat and a normal degree of humidity. l

HARRY T. BEBB. 

